Methyl silicon polymers and method of preparation



Patented Aug. 14, 1945 METHYL SILICON POLYMERS AND METHOD OF PREPARATION Rob Roy McGregor, Verona, and Earl Lcathen War-rick, Pittsburgh, Pa., Glass Works, Corning-N.

New York assignors to Corning Y., a corporation of No Drawing. Application July 26, 1943, Serial No. 496,210

Claims.

This invention relates to new compositions of matter, their preparation and uses, and, more particularly, to methyl silicon oxide polymers and their preparation.

This application is a continuationin-part of our copending application Serial Number 490520 filed June 11, 1943 and assigned to the assignee of the present invention.

Methyl silicon oxide polymers or methyl siloxanes as they are now commonly called are compositions which contain alternate silicon and oxygen atoms and methyl radicals attached to silicon through the carbon atom. They may be prepared either by hydrolysis of a hydrolyzable methyl-substituted silicane and condensation of. the hydrolysis product or by hydrolysis of a mixture of different hydrolyzable methyl-substituted silicanes and co-condensation of the hydrolysis products. By hydrolyzable methyl-substituted silicanes we mean methyl derivatives of SiHl which contain readily hydrolyzable radicals such as halogens, amino groups, alkoxy, aroxy, acyloxy radicals, etc. Examples of such compounds are methylsilicon trichloride, dimethylsilicon dichloride, trimethylsilicon chloride, methyltrieth oxysilicane, dimcthyldiethoxysilicane, trimethylethoxysilicane, etc.

Methyl silicon oxide copolymers have been prepared by the hydrolysi and condensation of mixtures of compounds of the formulaeCHaSiX: and (CH:)2SiX2, where X represents a readily hydrolyzable group of the kind named above. The products hitherto prepared in this manner have been thermally unstable liquids which when heated are readily converted to gels or resinous solids. It is highly desirable for certain purposes, such as high altitude flying, to flnd a hydraulic fiuid which is adapted to function eiiectively over a wide temperature range and particularly at temperatures below 40 C. Because of their thermal instability, use of the above methyl silicon copolymers as hydraulic fluids, damping fluids, etc has been too hazardous for their adoption commercially. It would be highly desirable to find one which is thermally stable and which other properties such as low solidification temperature, low vapor pressure, relatively 10w viscosity-temperature coefilcient and chemical stability.

One of the objects of our invention is to provide a thermally stable liquid methyl silicon oxide mlvm Another object of our invention is to provide a thermally stable methyl silicon oxide copolymer which consists of the structural units Another object of our invention is to provide a method of preparing a liquid methyl silicon oxide polymer which has a low solidification temperature, a low temperature-viscosity coefilcient and which does not readily set to a gel at elevated temperatures.

Another object of our invention is to provide a liquid methyl silicon oxide polymer having an average of between about 1.80 and about 1.95 methyl radicals per silicon atom.

Still another object of the present invention is to provide a liquid methyl silicon oxide polymer which has a solidification temperature of less than 80 C.

In accordance with our invention, we have provided a method of preparing a stable liquid methyl silicon oxide polymer which comprises cohydrolyzing and can-condensing a mixture of approximately 80 to 95 mol per cent of a hydrolyzable dimethyl silicane and approximately 5 to 20 of 2N HCl at such a rate that the Example 1 A mixture of .9 mol of dimethyldiethoxysilicane and .1 mol of monomethyltriethoxyailicane was dropped with stirring into half its volume did not rise above C. The whole then refluxed for four hours. An oil was produced which, after being washed with water and dried, had a viscosity of about Saybolt seconds at 86 F.

Example 2 The oil prepared in Example 1 was increased in viscosity to about 135 Saybolt seconds at 88' F. by passing a CO: stream through it at 100 mm. pressure to remove lower more volatile polymers.

Example 3 cm-r-r-o and o-a-o However, owing to the diiliculty of obtaining complete hydrolysis and complete condensation there may be present some unhydrolyzed ethoxy radicals or the like or some hydronl groups but not in suflicient amounts to impair the properties of the liquid products.

The following table shows the relative thermal stability of methyl silicon oxide copolymers prepared from difierent mixtures of monomethyltriethoxysilicane and dimethyldiethoxysilicane.

The first row gives the mol per cent of monomethyl compound present in the initial reaction mixture, the balance being the dimethyl compound. In item A are given the viscosities in centistokes of the copolymers as prepared prior to heat treatment. In item B are given the number of hours required to bring about gelation at 40 It will be seen from the above table that a. minimum solidification temperature is obtained in the range ofto10molpercentofofthemonomethyl compound.

The variation of viscosity with temperature has been measured for the copolymers having from about 1.80 to about 1.95 carbon atoms per silicon In all cases the slope is flatter than for a commonly used hydrocarbon oil, "Gulfpride 40. The following table shows the comparative change of viscosity with temperature of "Gulfpride 40" and a methyl silicon oxide copolymer formed from 90mol per cent of dimethyldiethonsilicane and 10 mol: per cent of methyltrlethoxysilicane. In this table, the temperature-memcientof viscosity or the change of viscosity with temperature is shown as the slope of the line given by plotting the logarithms of the viscosi y 9. as ordinates against the reciprocals of the absolute temperatures asabscissae. Hie lower the value of the slope between given temperatures, the smaller the change in viscosity of the material between these temperatures.

Table III A 2 *8 Solidifiea- A HT Liquid tion temperature m mas C. Win-5P0.

' c. "Gulfpride 40" -I9 2. 218 Copolymer (90-l0) M 710 1,111)

A comparison of the viscosity of a polymeric methyl siloxane of our invention having a ratio of 1.9 methyl groups per silicon with the viscosity of a high grade hydraulic oil from a petroleum 230 C. base is given in the following table.

Table I Percent mono (mob) o 2 5 1o 15 m an as an Alnitial viscosity, centistokes 42 23- 7 ill- 7 Hi 35.0 60.1 102.0 31.0 514 Gel B'Iime to get at hours-2M) C ll 16 26 2s 17 m 5 4 o The above table clearly shows the outstanding Table IV thermal stability of the copolymers containing not more than about 20 per cent of the mono- I methyl compound. Furthermore, samples of co- Methyl polymers within this range have been heated at pe me siiox ne dnulicoil 100 0. for over 600 hours without gelation. 48)

In the following table are shown the extremely m 7 low temperatures at which the copolymers of our 1m g invention solidify. These solidification tempera- 0 22 l we saw tures are equilibri m p r m at which 240:3:::3::::::::::::::::::::::::;3::::::: 21%

melting and freezing coincide if cooling is obtained by a liquid nitrogen bath (-195 C.) and heating by a dry ice acetone bath (-76 C.) or It will be seen from the above table that between by room temperature (25 C.) while stirring.

and 0 F., for example, the increase in vis- Tdble 11 Percent mono (mole) Solidifl r at aasaoaa cosity of the petroleum oil is nearly eight times that of the methyl siloxane.

The copolymers having a composition lying within the range or our invention are eminently adapted to be used as damping fluids for vibrating members or as hydraulic fluids for fluid pressure actuatable devices. Their low solidification temperatures, low vapor pressure, low viscosity temperature coeflicient and their thermal stability qualify them for these uses. In addition, they are chemically stable, being inert to oxygen, commonly used construction metals, plastics, and natural and synthetic rubber.

We claim:

1. In a fluid pressure actuatable device, a hydraulic fluid comprising a liquid polymeric methyl siloxane having an average of approximately 1.9 methyl groups per silicon atom and having a solidification temperature below 80 C. said siloxane consisting essentially of recurring structural units which correspond to the formulae CHaSiOm and (CH1) 2810, respectively, said-units being joined together by silicon-oxygen linkages.

2. In a fluid pressure actuatable device, a hydraulic fluid comprising a liquid polymeric met yl siloxane having an average of approximately 1.9 methyl groups per silicon atom and consisting essentiallyof recurring structural units which correspond to the formulae CHaSiO-m and (CH3) :SiO, respectively, said lmits being joined together by silicon-oxygen linkages.

3. In an apparatus for damping a vibrating member, a damping fluid comprising a liquid polymeric methyl siloxane having an average of approximately 1.80 to approximately 1.95 methyl groups per silicon atom and consisting essentially of recurring structural units which correspond to the formulae CHaSiOzn and (CHzOaSiO, respectively, said units being joined together by siliconoxygen linkages 4. The method of preparing a, liquid methyl silicon oxide copolymer which comprises mixing dimethyldiethoxysilicane with monometlrvltrithoxysilicane in the molar ratio of approximately 9 to 1, hydrolyzing the mixture with aqueous acid, condensing the methyl silicon hydrolysis product, recovering said condensed methyl silicon hydrolysis product and then passing carbon dioxide gas therethrough at elevated temperature and reduced presure toremove the volatilelower polymers.

5. The method of preparing a liquid methyl silicon oxide copolymer which comprises mixing dimethyldiethonsilicane with monomethyltriethoxysllicane in the molar ratio of approximately 9 to 1, adding the mixture slowly to hydrochloric acid while maintaining the temperature below 50C.,reiiuxlngthemixtureuntilanoilyprodnot is obtained and then washing and drying said product.

6. Liquid polymeric siloxane having an average of approximately 1.80 to approximatel 1.95 methyl groups per silicon atom and consisting essentially of recurring structural units which correspond to the formulae CHsSiOm and (CHshSiO, respectively, said units being joined together through silicon-oxygen linkages and said siloxane having a solidification temperature less than 80 C. and remaining liquid for at least 16 hours at 230 C. without gelation.

7. The method of preparing a methyl silicon oxide copolymer which comprises hydrolyzing a mixture consisting of 80 to 95 mol per cent of (CHhSiXz, the remainder being CHaSiYa, said hydrolysis being carried out in the presence of aqueous acid and condensing the methyl silicon hydrolysis product, where X and Y are readily hydrolyzable groups selected from the class consisting of halogens and alkoxy radicals.

8. The method of preparing a methyl silicon oxide copolymer which comprises hydrolyzing a mixture consisting of 80 to 95 mol per cent of dimethyldiethoxysilane, the remainder being methyltriethoxysilane, said hydrolysis being car- .ried out in the presence of acid and condensing the methyl silicon hydrolysis product.

9. Liquid polymeric methyl siloxane having an average of approximately 1.9 methyl groups per silicon atom andconsisting essentially of recurring structural units which correspond to the formulae CHsSiOs/z and (CHalrSiO, respectively, said units being joined together through siliconoxygen linkages, and said siloxane remaining liquid for at least 16 hours at 230 C. without gelation and having a solidification temperature between about 80 and about +90 C. and a viscosity temperature coemcient as represented by the expression 55 joined together by silicon-oxygen linkages.

ROB ROY MCGREGOR. EARL LEATHEN WARRICK. 

